This is an enumerated option, unspecified, retain, or no-retain, controlling whether a managed route stays in the forwarding table if the route manager process shuts down, versus being removed automatically. Choosing retain protects continuity of forwarding during a brief route-manager restart, while no-retain enforces that the route disappears immediately if its manager is gone. An admin who wants forwarding to keep working through a planned software restart on the virtual router would set critical managed routes to retain.